Used the stock MXL 2001 S.S. Transformer in a Royer Tube Mod and lots of hiss

I measured 48 ohms on one side and about 150 ohms on the other. I connected the 150 ohms side to the tube and the 48 ohms side to the XLR jack. I have NO idea on transformers or what I should expect. I do see on the MXL 2001 Schematic that there are some 42.5 ohm resistors in series with the transformer to each of the XLR pins 2 and 3. Also, according to the schematic I found, the ratio is 1.87:1.

Why am I getting so much hiss and is it the transformers fault? Is there anything I can do other than changing out the transformer?

It sounds pretty good, maybe a little thin if anything but not bad.

Turned out to be a bad tube. Put a new tube in there and it's nice and quiet and LOTS more gain.

Nice that you got it working! One observation though: the transformer ratio is too low. It should be at least 6:1 for 5840. With 1.87:1 ratio you definitely have a hot output, but the output impedance is too high. It can screw up the sound with some preamps. Maybe not with the one you're using.

I ended up changing out the transformer. I probably wouldn't have if I hadn't ran into the hiss problem but trying to fix that I bought a transformer 1:12 and it sounds much better than the stock with the wrong ratio.